124 Prof. Agassiz on Fossil Fishes. 



slimy and the soft rays are united into a single dorsal. The cheeks 

 and the body are covered with scales, which, according to my re- 

 searches, are characterized by their having few denticulations on 

 the posterior margin; moreover, this toothed structure is very weak, 

 and easily falls off. The Sparoidse are distinguished from the 

 ScicenoidcB by the absence of cavities in the bones of the head, by a 

 want of scales on the fins, by the absence of spines or of denticula- 

 tions on the opercular pieces. This latter character distinguishes 

 them likewise from the Percoidcey The genus Sciasnurus must, 

 therefore, be placed among the Sparoidse. Cuvier has divided this 

 family into several tribes, according to their dentition ; there is 

 only one, that of Dentex, which is entirely deprived of rounded 

 molars, and in which none but hooked and conical teeth, generally 

 arranged in a single row, are found. I have compared the skeleton 

 of Dentex vulgaris with that of Scisenurus. The same characters 

 are met with, but the division of the upper surface of the cranium 

 into three parts is not so marked, and the front is likewise not so 

 developed as in Scicenurus. However, the same keeled nasal is 

 found ; the parietal fossa3 form an elongated oblong, bordered by 

 two raised and thin parietal crests ; the temporal grooves are simi- 

 lar, and separated from the peculiar mastoidean grooves. We> more- 

 over, find in the Dentices the same form of the preoperculum, with 

 its vertical crest and its straight border ; and in the whole family of 

 the Sparoidce, the enormous suborbital which nearly hides the whole 

 of the superior maxillary. Cuvier distinguishes from the true 

 Dentices the genus Pentapodes, which comprises the species, having 

 the mouth less divided, with very scaly head, and caudal scaly to the 

 end. It is by the side of this genus that Scisenurus should be ar- 

 ranged; its compressed and raised body distinguishes it, while, in 

 the Pentapodes, the body is fusiform and elongated. It is, more- 

 over, characterized by its dentition ; the Dentices, like the Penta- 

 podi, have the teeth unequal ; the Pentapodi have two strong 

 canines, which are situated between several other smaller hooked 

 teeth, placed behind the teeth en velour ras. The genus Scisenurus 

 has no canines ; its teeth diminish equally from the front hindwards ; 

 they are all hooked ; but while approaching the Pentapodi by the 

 caudal, which has scales at the base, it is, on the other hand, related 

 to the Dentices by its compressed body. My genus Sparnodus, of 

 which I have described several species from Monte Bolca, likewise 

 approaches to the genus Scicenurus, by the uniformity of its teeth, 

 but it differs from it, in the teeth being short and very obtuse. 



1 am at present acquainted with two species of the genus Scise- 

 nurus, both derived from the London clay of Sheppey. 



It is necessary to guard against confounding the fragments of a 

 species of Myripristis with the Scicenuri, to which they approach, 

 considerably in their general form, but differ from them by the pron 

 minent striaa of the operculum, and by. the structure of the scales,. 



